A display device such as a liquid crystal display device, is provided with a large number of signal lines within a display region that is called as an active area. These signal lines are connected to external connecting terminals (terminals for receiving video signals output from a source driver IC mounted on the panel substrate, for example) disposed on a panel substrate. In the meantime, as to wiring between the active area and the external connecting terminals, as illustrated in FIG. 22, a wiring structure in a fan shape on a plane surface of the panel substrate is often employed.
In recent years, demands for downsizing of display devices have become increased. However, employment of a wiring structure as illustrated in FIG. 22 tends to increase a size of a picture-frame. In particular, when the number of signal lines provided within the active area increases due to increased resolution, a size of a picture-frame increases remarkably. An increase in the size of a picture-frame as described above makes downsizing of display devices difficult.
Thus, it is proposed to employ a layered structure having two or more layers for wiring between external connecting terminals and an active area. Here, the following description is given focusing on source bus lines (video signal lines) for transmitting video signals, among signal lines provided in the active area. FIG. 23 is a plan view illustrating one example of a conventional layered wiring structure. FIG. 24 is a diagram for detailed description of the wiring structure shown in FIG. 23. FIG. 23 shows source bus lines SL1 to SL12 of a first column to a twelfth column among a plurality of (e.g., 960) source bus lines disposed extending from external connecting terminals to the active area. It should be noted that, in the following description, the source bus lines are denoted by a reference character SL when the source bus lines do not need to be distinguished from each other.
The wiring structure illustrated in FIG. 23 and FIG. 24 is configured by wiring lines (first-layer wiring lines) K1 provided in a first layer (a lower layer in this case) and wiring lines (second-layer wiring lines) K2 provided in a second layer (an upper layer in this case). One (the source bus line SL2 in FIG. 24) of two adjacent source bus lines is configured only by a first-layer wiring line K1. The other (the source bus line SL1 in FIG. 24) of the two adjacent source bus lines is configured by the first-layer wiring line K1 and a second-layer wiring line K2. The first-layer wiring lines K1 and the second-layer wiring lines K2 are connected by contacts CT, respectively. Within a region denoted by a reference character 92 in FIG. 24, the first-layer wiring line K1 and the second-layer wiring line K2 are arranged so as to be overlapped with each other in a vertical direction (up-down direction). Here, an insulating layer (not shown) is disposed between the first-layer wiring line K1 and the second-layer wiring line K2.
By arranging the plurality of source bus lines SL so as to be overlapped with each other in the vertical direction as described above, it is possible to reduce the size of a picture-frame as compared to the case in which a wiring structure illustrated in FIG. 22 is employed. A display device having a layered wiring structure in this manner is disclosed, for example, in Japanese Laid-Open Patent Publication No. 05-19282.